Contact Information:
Phillip J. Clauer
Senior Extension Associate
4-H Youth and Specialty Poultry
Department of Poultry Science
The Pennsylvania State University
Biology of the Fowl
Let's take a look at the internal and external biology of the chicken. The chicken is an interesting creature when observed from a biological standpoint. The chicken has a comb, which is unique. It has a high rate of metabolism, is a rapid breather and digests its food relatively quickly. The body temperature varies, but averages around 106°F. Let's start with the terms for the chicken's exterior features.
Interesting Facts About
The Exterior Features Of The Chicken
The Comb of a chicken functions as its cooling system. Chickens do not sweat like humans. The chicken cools itself by circulating its blood throughout its comb and wattles. The comb in ascent operates like the radiator in a car. There are seven different types of combs in chickens. The four most common types of combs are shown in Figure 1.
The Earlobe color can tell you what color egg the chicken will lay. If the chicken has a white earlobe, it will lay a white-shelled egg. If it has a red earlobe, it will lay a brown-shelled egg. There is one exception of this rule: Araucana lay blue and green-shelled eggs.
By observing the Hackle (neck) and Saddle (back) feathers of an adult chicken, you can determine its sex. Male hackle and saddle feathers come to a distinctly pointed tip and are shinier. Female hackle and saddle feathers have rounded ends. The breeds of "Sebright" and "Campine" are the only exceptions. In these two "hen-feathered" breeds, the feathers are alike in both sexes.
Although feathers come in many color patterns (Figure 2 shows some for the feather patterns you will find in purebred chickens). Feathers basically serve as the bird's protection. They can insulate the bird from the cold, protect the bird's skin from getting wet and can help the bird fly or glide to safety. Although feathers cover most of a bird's body, they all grow from certain defined areas of the bird's skin called "feather tracts". The first indications of feather tracts appear during the fifth day of embryonic development when the feather papillae appear. Papilla is Latin for "pimples" and that is what they look like on a developing embryo.
The Skeleton of the fowl is compact, lightweight, and strong. Birds have many hollow bones that are connected to the respiratory system; these are the bones of the skull, humerus, clavicle, heel, and lumbar and sacral vertebrae. Another interesting feature of chicken bones is called medullary bone. This bone fills the narrow cavity with a readily available source of calcium for eggshell formation when calcium intake is not sufficient. Medullary bone is found in the tibia femur, pubic bones, sternum, ribs, ulna, toes and scapula (see Figure 4).
Chicken Digestive System
The chicken has a simple digestive system, with few to no microorganisms living in the digestive system to help digest food like in ruminants such as cattle. Chickens depend on enzymes to aid in breaking down food so it can be absorbed, much like humans.
The beak of the bird replaces the mouth and lips. The crop is a pouch formed to serve as a storage area for the food until it can be passed along for digestion in the gizzard and intestines. The proventriculus is the true stomach of the bird from which hydrochloric acid and pepsin (an enzyme) is secreted to aid in digestion. The gizzard is the oval organ composed of two pairs of thick red muscles. These muscles are extremely strong and are used to grind or crush the food particles. This process is aided by the presence of grit and gravel picked up by the bird. The digestion and absorption of food takes place primarily in the small intestine. It usually takes about 2.5 hours for food to pass through the digestive tract from beak to cloaca.
Figure 1 Comb types of Chickens
Figure 2 Feather patterns found in Chickens
Figure 3 Chicken External Anatomy
Figure 4 Chicken Skeleton